The increased incidence of morbidity from hypertension in the black population of the U.S.A. has been well documented but not explained. One reason for this is our lack of knowledge of cardiovascular events outside the laboratory. While the indirect method gives good data for epidemiological screening and large drug trials, its inaccuracies are too great for assessment of the individual subject. A direct method of recording the arterial blood pressure and electrocardiogram from ambulant out-patients, while attending their normal duties, has been developed and used extensively by the applicant. The recorder will acquire continuous blood pressure and heart rate data for a complete 24-hour period. This system is to be used to compare the cardiovascular events and mean pressures and rates in a group of black and white hypertensives. The responses to standard antihypertensive therapy will also be studied and compared. It is, thus, planned to develop a more rational approach to the treatment of hypertension in both populations.